Transition detection at input of integrated circuit device

ABSTRACT

An integrated circuit has an input connection for connecting an external signal conductor that passes signals to execute functions in the device. The external signal conductor can pick up strong interfering signals with high frequency content, for example when the device is used in a car. To protect against unintended execution of functions the device contains a timer circuit comprising a capacitance and a current supplying circuit coupled to an integration node. A discharge diode is coupled between the input connection and the integration node, with a polarity such that the discharge diode, when in forward bias, is capable of draining current from the current supplying circuit. A detector is coupled to the integration node for generating a signal to be supplied to the integrated circuit device to respond to a signal transition on the conductor. The diode serves to reset integration on the integration node before the detector detects the transition in case of short pulses. By using a diode instead of a switching transistor the circuit is more robust against the effect of interfering pulses.

The invention relates to an integrated circuit device and moreparticularly to the detection of signals at an input of such a device.

An integrated circuit device has to receive input signals from circuitsoutside the integrated circuit device. These outside circuits areconnected to the integrated circuit device via relatively longconducting wires. In some cases the integrated circuit device has tooperate in very hostile circuit environments, where the conducting wirescan pick-up strong unwanted signal pulses. In cars for example (moregenerally in automotive environments) unwanted signal pulses can have abandwidth of I GHz or more and amplitudes of tens of volts. In such ahostile environment the unwanted pulses are difficult to suppress,because they have a tendency to penetrate the circuit in an uncontrolledway via parasitic pathways.

The unwanted signal pulses can be distinguished from normal signals onthe conductor on the basis of duration. Only signals with pulses thatlast longer than all or most of the pulses of the unwanted signal areused as normal signals. To eliminate unwanted pulses on the basis ofduration, passive linear low-pass filters may be used which are made upof resistors and capacitors to filter out unwanted signal pulses.However, passive linear low-pass filters that use resistors andcapacitors to filter out pulses require relatively large capacitors.When integrated in an integrated circuit such capacitors take upvaluable space in the integrated circuit.

U.S. Pat. No. 5,794,055 shows an alternative approach in a circuit foruse in an automotive environment where an external wake-up signal isused to trigger an interrupt to a microprocessor circuit in anintegrated circuit device. The wake-up signal is generated by closing aswitch that is connected to an input connection of the circuit. Tosuppress noise, the wake-up signal is not converted to an interruptsignal immediately after detection of an input signal that correspondsto closing of the switch. Rather, with a delay after detection of theinput signal, the circuit starts applying a diagnostic current to theinput connection. The interrupt is applied to the microprocessor only ifthe response to the diagnostic current confirms that the switch isclosed.

For its normal signal operation, excepting noise suppression, U.S. Pat.No. 5,794,055 describes various circuits with resistors and capacitors,for example, a signal conditioner circuit with a low-pass filter andvoltage divider function. The input of this conditioner circuit iscoupled to the switch via a blocking diode, which comes into conductionwhen the switch is closed to indicate a wake-up signal. The conditionercircuit acts as a low-pass filter and voltage divider of the signalgenerated by closing the switch before that signal is applied to aninput of a microcontroller. The blocking diode prevents any influencevia the input that is connected to the switch when the switch is notclosed.

When integrated in an integrated circuit, passive linear low-passfilters that use resistors and capacitors to filter out pulses requirerelatively large capacitors and/or resistors. An alternative techniqueto filter out pulses uses a timer circuit. FIG. 1 shows a conventionaltimer circuit applied to detect an input signal. In the timer circuitthe signal at the input connection 10 is used to start and resetintegration in an integrating circuit 12, in which a charging capacitor14 coupled to an integrating node 16 is charged by a current supplyingcircuit 15. A comparator 18 is coupled to the integrating node 16. Whenthe integrated voltage at the integrating node reaches a threshold, thedetector passes a signal, such as a wake-up signal, to further circuits19. An unwanted short pulse has no effect because, although the start ofsuch a short pulse starts integration, a reset occurs before theintegrated voltage can reach the threshold.

In a timer circuit the signal at input connection 10 is not directlypassively filtered to suppress short duration pulses. Insteadtransitions in the signal at the input connection are used to start andreset integration. The integration speed itself is determinedsubstantially independently of any current to the input connection bythe capacitance value of the charging capacitor 14 and the currentsupplying circuit. As a result, a much smaller capacitor 14 can be usedin the integrating circuit than in a passive linear low-pass filter.

The function of starting and resetting integration is usuallyimplemented by arranging the main current channel of a switchingtransistor 11 in parallel with the charging capacitor 14, and applying asignal derived from the input connection of the integrated circuitdevice to the control electrode of the switching transistor so as todischarge the charging capacitor 14 outside the pulses.

However, such an implementation of the start and reset function hasturned out to be vulnerable in hostile environments, such as automotiveenvironments. When the duration of unwanted pulses approaches the delayof the switching transistor 11 it becomes possible that integrationcontinues in spite of the short duration of the unwanted pulses, becausethe switching transistor 11 does not become properly conductive.Similarly, parasitic capacitances in the switching transistor 11 maylead to unwanted integration effects.

Among others, it is an object of the invention to provide an integratedcircuit device with a connection for an external conductor that permitsdetection of signals from the conductor, while effectively suppressingunwanted signals without using large capacitors for passive low-passfilter purposes.

The invention provides an integrated circuit according to claim 1. Theintegrated circuit device according to the invention uses a timercircuit to eliminate unwanted pulses of short duration. According to theinvention a diode is used between the input connection of theintegrating circuit and the integration node of the timer circuit, sothat the diode serves to reset integration at the end of a pulse thathas a polarity that would normally lead to passing of a pulse detectionsignal from the comparator, if the pulse is sufficiently long. By usinga diode for this purpose, the problems associated with a resettransistor are avoided. A diode provides a maximum speed reset withreduced susceptibility to disturbance by unwanted pulses. To achieveoptimum speed, preferably no resistance is included in series with thediode between the input connection and the integration node, or aresistance is included that does not reduce the speed of discharge ofthe charging capacitor to substantially below the speed of the detectorcircuit.

In an embodiment, a first and a second integrating circuit forintegration with mutually opposite integration polarity are included,each containing a diode that serves to reset integration, the diodes inthe integrating circuits being coupled with mutually opposite polarity.First and second detectors of the integrating circuits are coupled to amemory element that is set to a first state after detection integrationof the first integrating circuit crosses a first threshold and to asecond stage after detection integration of the first integratingcircuit crosses a second threshold. Thus, short unwanted pulses wherethe signal goes low as well as short unwanted pulses where the signalgoes high are eliminated. Preferably, the thresholds are offset at leasttwo diode voltage with respect to one another, so that conflicts betweenthe detectors are excluded.

Preferably a switchable current source is provided, having a currentoutput coupled to the input connection, for forward biasing the diode,the switchable current source having a switching control input coupledto the state holding circuit for switching the switchable current sourceoff when the state holding circuit is set to the first state andswitching it on when the state holding circuit is set to the secondstate. The switchable current source provides for a time selectivethreshold against detection of weak pulses of one polarity when thecircuit is receptive for detecting pulses of that polarity. Preferably,two current sources of opposite polarity are provided in this way forproviding mutually opposite thresholds when the state holding circuit isin the first and the second state, respectively.

The circuit is particularly useful in an automotive environment (forexample in the electronics system of a car) since it has been found thatintegrated circuits often disfunction in such an environment due tounwanted signal pulses.

Preferably, a wake-up input connection of an integrated circuit isprovided with a circuit as described above. A wake-up input is used toswitch an electronic circuit from a “sleep” state in which many parts ofthe circuit are disabled to reduce power consumption to a normaloperating state where these parts are enabled. Wake-up signals oftencome from remote locations and therefore wake-up inputs often have to beconnected to long conductors, which makes protection against unwantedpulses especially advantageous.

FIG. 1 shows a prior art integrating circuit connected to an inputconnection,

FIG. 2 shows a circuit with an input protection circuit,

FIG. 3 shows signals that occur in the circuit of FIG. 2,

FIG. 4 shows a two way input protection circuit,

FIG. 5 shows a detailed circuit with an input protection circuit, and

FIG. 6 shows a car with an electronic control system.

FIG. 2 shows a circuit with an input protection circuit. The circuit isintegrated in an integrated circuit device, typically a semiconductorintegrated circuit device. The circuit contains an input connection 20of the integrated circuit device, such as a bond pad, for connection ofan external conductor. The circuit furthermore contains a diode 21, adetector circuit, further circuits 29 and an integrating circuit 22 witha charging capacitor 24, a current source circuit 25 and a changing node26. Input connection 20 is coupled to charging node 26 via diode 21,diode 21 being arranged with a polarity such that it is able to draincurrent from current source circuit 25 in a forward direction. Chargingnode 26 is coupled to a first power supply line Vgnd via chargingcapacitor 24 and to a second power supply line Vbatt via current sourcecircuit 25. Charging node 26 is coupled to an input of detector 28,which has an output coupled to further circuits 29. Charging capacitor24 should withstand the voltages that are present on node 20; for highervoltages this may be realized by using a pair of conductive planes inthe interconnect wiring of the integrated circuit device, which areseparated by a dielectric layer. Charging capacitor 24 has a capacitanceof around 1 pF for example. Diode 31 may be implemented for example as alateral diode in a semiconducting layer of the integrated circuitdevice.

FIG. 3 illustrates the operation of the circuit of FIG. 2. FIG. 3 showsan input signal 30 at input connection 20, an integrated voltage 32 atcharging node 26, and an output signal at the output of detector 28.Input signal 30 initially has a low voltage, but the voltage rises to ahigher level during a relatively long pulse 36. Later, input signal 30again rises, but only for a relatively short pulse 38. As long as inputsignal 30 has a low voltage, diode 21 keeps charging capacitor 24discharged.

When the voltage of input signal 30 rises during a pulse 36, 38, acurrent I from current source circuit 25 starts charging capacitor 24 sothat the voltage Vn 32 at charging node 26 starts rising according todVn/dt=I/C, where C is the capacitance value of charging capacitor 24.When input signal 30 drops back again, the charging current is deviatedfrom charging capacitor 24 and charging capacitor 24 is discharged.

Detector 28 generates a signal transition at its output when its inputvoltage (integrated voltage 32) crosses a threshold voltage level 39.During a relatively long pulse 36, integrated voltage 32 continues torise until it reaches threshold voltage level 39. Accordingly detector28 generates a signal indicating detection of the pulse. After arelatively short pulse 38, charging capacitor 24 is discharged beforeintegrated voltage 32 rises to threshold voltage level 39. As a result,detector 28 produces no detection signal and further circuits 29 are notinformed of relatively short pulse 38.

Further circuits 29 are arranged to respond to the detection signal thatdetector 28 generates when integrated voltage 32 rises over thresholdvoltage level 39. This does not occur when a pulse 38 at inputconnection 20 is relatively short. The critical length of the pulse isdetermined by threshold voltage level 39 and the integration speed(which depends on the current from current source 25 and the capacitancevalue of capacitor 24). Currents through diode 21 do not substantiallyaffect this critical length: diode 21 only provides for a reset of theintegration when the pulse terminates.

FIG. 4 shows a two-way protection circuit. In addition to the componentsshown in FIG. 3, the circuit contains a further integrating circuit witha further diode 41, a further charging capacitor 44, a further currentsource circuit 45, a further detector 48 and a further charging node 46.Current source circuit 25 and further current source circuit 45 supplycurrents to their respective charging nodes 26, 46 in mutually oppositedirections. Further diode 41 is coupled between further charging node 46and input connection 20 with a polarity opposite to that of diode 21, sothat further diode 41 is capable of draining current from furthercurrent source circuit 45 in the forward direction. A further detector48 has an input coupled to further charging node 46.

The circuit contains a set/reset flip-flop 42 with a set and a resetinput coupled to the outputs of detector 28 and further detector 48respectively, and an output coupled to further circuits 43, whichinclude a microprocessor for example. Detector 28 and further detector48 are designed to set and reset flip-flop 42 when the integratedvoltage at charging node 26 and further charging node 46 rises above anddrops below a threshold level respectively.

In operation, relatively long pulses of the type shown in FIG. 3 causeflip-flop 42 to be reset. Relatively long pulses with opposite polarity(from a high voltage level to a low voltage level and back) causeflip-flop 42 to be set. For each type of pulse, a diode 21, 41 is usedto discharge a charging node 26, 46, but with opposite polarity. Whenthe rising integrated voltage at charging node 26 is not reset before itcrosses the threshold level of detector 28 flip-flop 42 is set. When thedropping integrated voltage at further charging node 46 is not resetbefore it crosses the threshold level of further detector 48 flip-flop42 is reset.

Thus, the state of flip-flop 42 is affected by transitions of twoopposite types of polarity at input connection 20, from low to high andfrom high to low, provided that these transitions are not the leadingtransition of a pulse with a duration below a threshold duration.

Setting and resetting occur in response to pulses of either type onlywhen the duration of the pulses exceeds critical lengths for therespective type of pulse. The critical lengths of the pulses aredetermined by threshold voltage levels of detectors 28, 48 and theintegration speeds of the integrating circuits (which depend on thecurrent from current source circuits 25, 45 and the capacitance value ofcapacitors 24, 44). Currents through diodes 21, 41 do not substantiallyaffect this critical length: diodes 21, 41 only provide for a reset ofthe respective integrations when the pulses terminate.

It will be appreciated that the invention is not limited to the circuitof FIGS. 2 and 4. For example, instead of current source circuits 25, 45other current supplying circuits may be used, such as resistances, aslong as such circuits permit a rising or decreasing voltage to developwhen their diode is reverse-biased. Similarly, charging capacitors maybe implemented by any circuit with a capacitive effect and with theplate opposite to the charging node connected to any voltage supply.However, preferably conductive (not semi-conductive) plates are used,separated by a layer that can withstand relatively high capacitorvoltages, since in a hostile environment signals from input connection20 may penetrate the capacitors. When current mirrors are used toimplement current source circuits 25, 45, these current mirrorspreferably have their own input transistors (not shared with othercircuits) to prevent unwanted high frequency signals at input connection20 from affecting such other circuits. Instead of a flip-flop, anycircuit may be used that can be set to at least two different states. Toachieve optimum speed preferably no resistance is included in serieswith diode 21 between input connection 20 and integration node 26.However, without detrimental effect a small resistance could be usedthat does not decrease the speed of discharge of charging capacitor 24substantially below the speed of detector circuit 28.

FIG. 5 shows a more detailed circuit. In comparison with FIG. 4,controllable current sources 50, 52 have been added between inputconnection 20 and the different power supply connections Vgnd and Vbatt,respectively. Controllable current sources 50, 52 receive controlsignals from flip-flop 42. Furthermore, the detectors have beenimplemented as comparators 58, 59, which provide for different detectionthresholds receive (by setting different reference voltages, assymbolized by the use of a common voltage source 54, a threshold raisingvoltage source 56 for the comparator that detects low to high pulses anda threshold-lowering voltage source 57 for the comparator that detectshigh to low pulses).

The circuit of FIG. 5 provides for two independent improvements.Controllable current sources 50, 52 provide for a current threshold ofpulses at input connection 20. Current thresholds work for both positiveand negative pulses because the current source that is connected to thepositive power supply is activated when a high level of sufficientduration has been detected, and the current source that is connected tothe negative power supply is activated when a low level of sufficientduration has been detected. Thus, disturbing signals of small strengthat input connection 20 are not detected. Preferably, controllablecurrent sources 50, 52 are implemented as current mirror circuits.Preferably, these current mirrors have their own input transistors (notshared with other circuits) to prevent unwanted high frequency signalsat input connection 20 from affecting such other circuits.

The use of different thresholds for comparators 58, 59 ensures that noconflicting set and reset signals are provided to flip-flop 42, even ifslow voltage variations occur at input connection 20. During slowvariations, both diodes 21, 41 are forward-biased. The voltage atcharging node 26 is one diode voltage drop higher than the voltage atinput connection 20 and the voltage at further charging node 46 is onediode voltage drop lower than the voltage at input connection 20. Thethreshold levels are set so that no simultaneous set and resetoccurrences take place, by setting the threshold of the comparator 58 ofthe further charging node 46 lower than the threshold of the othercomparator 59 of the charging node 26 by an amount that is at leastequal to the sum of the forward voltage drops over the diodes, typicallyat least 1.3 Volts in case of silicon diodes. Thus, no simultaneous setand reset occurrences can take place. This maybe realized for example byusing diodes to implement offset voltage sources 56, 57.

FIG. 6 shows a car 60 with an electronic control system. The electroniccontrol system contains a first unit 62 and a second unit 64 coupled viaa signal conductor 66. Second unit 64 contains an integrated circuitdevice of the type shown in FIGS. 2, 3 or 5, with input connection 20coupled to signal conductor 66. A return circuit (ground) between firstunit 62 and second unit 64 is realized via a common conductor 68, whichalso provides the return circuit of other circuits (not shown), forexample via the chassis of car 60.

First unit 62 is for example a switch for applying a signal to amicroprocessor in the integrated circuit device in second unit 64, forexample to control a motor to open a window. The first unit 62 is remotefrom the second unit 64, so that the signal conductor spans a muchlarger distance than the internal size of the units. In thisenvironment, signals at the second unit may contain strong unwantedsignals with high frequency content, due to currents from other circuits(not shown) on common conductor 68 or pick-up by signal conductor 66. Byusing the circuits shown, the risk of malfunctioning of the integratedcircuit device due to these unwanted signals can be reduced.

1. An integrated circuit device comprising: an input connection forconnecting an external signal conductor; a timer circuit comprising acapacitance and a current supplying circuit coupled to an integrationnode; a discharge diode coupled between the input connection and theintegration node, with a polarity such that the discharge diode, when inforward bias, is capable of draining current from the current supplyingcircuit; and a detector coupled to the integration node for generating asignal to be supplied to the integrated circuit device to respond to asignal transition on the conductor when a voltage of the integrationnode passes a threshold value due to integration of a current suppliedby the current supplying circuit when the discharge diode is in reversebias.
 2. An integrated circuit device according to claim 1, comprising:a further timer circuit comprising a further capacitance and a furthercurrent supplying circuit coupled to a further integration node forcharging the further integration node in a direction opposite to thedirection of charging of the integration node by the current supplyingcircuit; a further discharge diode coupled between the input connectionand the farther integration node, with a polarity such that the furtherdischarge diode, when in forward bias, is capable of draining currentfrom the further current supplying circuit; a further detector with aninput coupled to the further integration node; and a state holdingcircuit, coupled to the detector and the further detector, so that thestate holding circuit is set to a first and a second state by thedetector and the further detector, respectively, in response to signaltransitions on the conductor, when a voltage of the integration node andthe further integration node pass a threshold value and a furtherthreshold value due to integration of a current supplied by the currentsupplying circuit or the further current supplying circuit when thedischarge diode or the further discharge diode respectively is inreverse bias.
 3. An integrated circuit device according to claim 2,comprising a switchable current source having a current output coupledto the input connection for forward biasing the diode, the switchablecurrent source having a switching control input coupled to the stateholding circuit for switching off the switchable current source when thestate holding circuit is set to the first state and switching it on whenthe state holding circuit is set to the second state,
 4. An integratedcircuit device according to claim 2, wherein the detector and thefurther detector have mutually offset threshold levels, so that noupdate of the state holding circuit occurs when a difference betweenvoltages at the charging node and the further charging node is less thana sum of forward biased diode voltages of the discharge diodes seenbetween the charging node and the further charging node.
 5. Anintegrated circuit device according to claim 1, wherein an output of thedetector is coupled to a wake-up input of a data processing circuit inthe integrated circuit device.
 6. An integrated circuit device accordingto claim 2, wherein a state signaling output of the state holdingcircuit is coupled to a wake-up input of a data processing circuit inthe integrated circuit device.
 7. Electronic control system of a car,comprising a signal conductor between substantially different locationsin the car, and an integrated circuit device according to claim 1 withits input connection coupled to the signal conductor.